Polymérisation anionique | EPFL Graph Search

La polymérisation anionique est un type de polymérisation ionique dans lequel le centre actif est de nature anionique. Elle est constituée de l'amorçage, la propagation, éventuellement de transfert et de terminaison. Les monomères concernés sont ceux qui possèdent des groupements électro-attracteurs. Ce mode de polymérisation est utilisé avec les alcènes substitués comme le méthylpropène. La réaction de propagation est la suivante (pour le méthylpropène): :R− + CH2=C(CH3)2 → R-CH2-C−(CH3)2 La polymérisation anionique présente un certain nombre de difficultés. Parmi celles-ci, l’amorçage est une étape cruciale car il doit être rapide par rapport à l’étape de propagation afin de conserver des indices de polymolécularité faibles, et donc d'obtenir des polymères de masses molaires bien définies. Amorçage L'amorçage peut se faire avec une base forte, comme les hydroxydes, les alcoolates, les amidures.. Cette étape permet d'obtenir le centre actif : la charge négative sur l

Synthesis of silicone elastomers containing trifluoropropyl groups and their use in dielectric elastomer transducers

Yee Song Ko

Vinyl end-functionalized polysiloxanes P-x containing varying mol% of trifluoropropyl groups (x) were prepared starting from 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisiloxane (F-3) and octamethylcyclotetrasiloxane (D-4) via anionic polymerization in the presence of tetramethylammonium hydroxide (TMAH) and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane end-capping reagent. Their structures were determined by H-1 NMR spectroscopy and their molecular weights and distributions were measured by GPC. The various P-x were cross-linked in thin films via hydrosilylation of the vinyl groups with tetrakis(dimethylsiloxy) silane cross-linker in the presence of Karstedt catalyst. The mechanical, dielectric and electromechanical properties of the prepared films were investigated. An increase in the permittivity (epsilon') with increasing content of polar trifluoropropyl groups was observed with a maximum value of epsilon' = 6.4 for P-58(0). A maximum lateral actuation strain of 5.4% at an electric field as low as 7.8 V mu m(-1) was measured for a material prepared by cross-linking P-53.

Royal Soc Chemistry2015

Polypeptide brushes grown via surface-initiated ring-opening polymerization of alpha-amino acid N-carboxyanhydrides

Harm-Anton Klok

Polypeptide brushes are attractive platforms to generate functional and responsive interfaces that are of potential interest due to their possible biodegradability, biocompatibility and tunable secondary structures. Surface-initiated ringopening polymerization (SI-ROP) of alpha-amino acid N-carboxyanhydrides represents a powerful and versatile strategy to generate polypeptide brushes. This review is an attempt to capture the state-of-the-art in this field and highlights the latest developments in several selected areas. In addition to presenting an overview of the synthetic methods that have been used to generate polypeptide brushes via SI-ROP, this article will discuss the preparation of patterned polypeptide brushes, the conformational properties of surface-tethered polypeptides, ways to control chain orientation at surfaces as well as properties and applications of these thin polymer films.

Springer Verlag2015

Shape-Persistent, Thermoresponsive Polypeptide Brushes Prepared by Vapor Deposition Surface-Initiated Ring-Opening Polymerization of alpha-Amino Acid N-Carboxyanhydrides

Solenne Desseaux, Harm-Anton Klok

Surface-grafting thermoresponsive polymers allows the preparation of thin polymer brush coatings with surface properties that can be manipulated by variation of temperature. In most instances, thermoresponsive polymer brushes are produced using polymers that dehydrate and collapse above a certain temperature. This report presents the preparation and properties of polymer brushes that show thermoresponsive surface properties, yet are shape-persistent in that they do not undergo main chain collapse. The polymer brushes presented here are obtained via vapor deposition surface-initiated ring-opening polymerization (SI-ROP) of gamma-di- or tri(ethylene glycol)-modified glutamic acid N-carboxyanhydrides. Vapor deposition SI-ROP of gamma-di- or tri(ethylene glycol)-modified l- or d-glutamic acid N-carboxyanhydrides affords helical surface-tethered polymer chains that do not show any changes in secondary structure between 10 and 70 degrees C. QCM-D experiments, however, revealed significant dehydration of poly(gamma-(2-(2-methoxyethoxy)ethyl)-l-glutamate) (poly(L-EG(2)-Glu)) brushes upon heating from 10 to 40 degrees C. At the same time, AFM and ellipsometry studies did not reveal significant variations in film thickness over this temperature range, which is consistent with the shape-persistent nature of these polypeptide brushes and indicates that the thermoresponsiveness of the films is primarily due to hydration and dehydration of the oligo(ethylene glycol) side chains. The results presented here illustrate the potential of surface-initiated NCA ring-opening polymerization to generate densely grafted assemblies of polymer chains that possess well-defined secondary structures and tunable surface properties. These polypeptide brushes complement their conformationally unordered counterparts that can be generated via surface-initiated polymerization of vinyl-type monomers and represent another step forward to biomimetic surfaces and interfaces.

Amer Chemical Soc2015

Shape-Persistent, Thermoresponsive Polypeptide Brushes Prepared by Vapor Deposition Surface-Initiated Ring-Opening Polymerization of alpha-Amino Acid N-Carboxyanhydrides

Solenne Desseaux, Harm-Anton Klok

Amer Chemical Soc2015